A Colorado sheriff said firefighters "are getting the upper hand'' on the most destructive wildfire in state history Saturday, an announcement that came as authorities gained a clearer picture of the grim landscape the blaze has left behind.

No additional homes were destroyed as fire crews expanded containment lines, El Paso County Sheriff Terry Maketa said. Also, there were no new reports of injury or death, he said.

The fire that exploded Tuesday outside of Colorado Springs, amid record-setting heat and tinder-dry conditions, has destroyed nearly 500 homes and killed two people, whose bodies were found inside their garage Thursday, with their car doors open as though they had been about to flee.

On Saturday, worried residents waited for permission to return to their neighbourhoods to see whether their homes were still standing.

Maketa said the fire's destruction has made it difficult for his deputies to assess damage.

Firefighters advance containment on Colorado wildfire

"It looks like a nuclear bomb went off in some of those areas, and you can't even recognize whether it was a house or some other kind of structure,'' Maketa said. "That is the level of incineration and destruction that took place in some areas.''

Containment is at 45 per cent, an increase from 30 per cent on Friday. It's unknown what sparked the blaze, but investigators believe it was human-caused. So far, it's cost more than $3.5 million to fight.

Most mandatory evacuation orders have been lifted, as the fire zone remained at more than 6000 hectares.

Elsewhere in Colorado, fire crews worked to contain other smaller wildfires.

In Canon City, 80 km southwest of Black Forest, the Royal Gorge Fire burned 1300 hectares and was 65 per cent contained.

A lightning-sparked fire in Rocky Mountain National Park had burned more than 200 hectares and was 30 per cent contained.